The report gives results of a calibration study to determine sizing parameters and wall losses for five commercially available cascade impactors. A vibrating-orifice aerosol generator was used to produce monodisperse ammonium fluorescein aerosol particles 15 to 1 micrometers in diameter. A pressurized Collison Nebulizer system was used to disperse Dow Corning polystyrene latex (PSL) spheres 2 to 0.46 millimeters in diameter. When ammonium fluorescein was used, the mass collected by each impactor surface was determined using absorption spectrophotometry of washes from the various surfaces. When sizing with the PSL spheres, a Climet Instruments Model 208A Particle Analyzer was used to determine particle number concentrations at the inlet and the outlet of the test impactor. Results are reported showing stage collection efficiency as a function of the square root of the Stokes number, stage collection efficiency as a function of particle size, and impactor wall losses (total, nozzle, and inlet cone) as a function of particle size. It has been determined that the values of the Stokes number for the 50% collection efficiency are not generally the same for each impactor stage. A table of these values is presented. Published theories do not successfully predict these values, so empirical calibration is required before these devices can be used accurately in the field or laboratory.

Contract no. 68-02-0273, ROAP no. 21ADM-011, program element no. 1AB012. Issued Oct. 1976. Includes bibliographical references (p. 78).